Epicardial Mesothelial Cyst Located over the Left Anterior Descending Coronary Artery

Abstract

We report the 5th case of pericardial cyst found to originate from epicardium. A 30-year-old woman with a history of rheumatic fever underwent open-heart surgery for severe aortic and mitral insufficiency. A cyst located over the left anterior descending coronary artery was detected during surgery. Excision of the cyst was performed with the patient on cardiopulmonary bypass, to avoid injury to the artery. Histologic examination showed the cyst to be lined by a single layer of benign mesothelial cells, which was consistent with a diagnosis of epicardial mesothelial cyst.

Although several pericardial cysts have been reported in the English medical literature,^1–3 only 4 such cysts have originated from the epicardium.^4–7 These are benign cysts, which are usually detected incidentally. They are easily excised, except when they are located near important cardiac structures.

In September 2003, a 30-year-old woman was referred to our department of cardiovascular surgery with a diagnosis of severe aortic and mitral valve insufficiency. Her chief complaints were dyspnea on exertion, fatigue, and palpitations. The patient was in New York Heart Association functional class III. She had a history of rheumatic heart disease. A pansystolic murmur, loudest at the apex, and a pandiastolic decrescendo murmur, loudest over the left lower sternal border, were detected on auscultation. Water-hammer pulse was identified on palpation. Chest radiography revealed an enlarged left atrium and left ventricle. The electrocardiogram showed left atrial overload and left ventricular hypertrophy. Atrial fibrillation was present. Echocardiographic findings were severe mitral valve insufficiency, moderate-to-severe aortic insufficiency, giant left atrium, and enlarged left ventricular dimensions. Angiography demonstrated severe aortic and mitral valve insufficiency; the coronary arteries were normal.

At surgery, the pericardium was adherent to the heart, possibly due to a previous episode of pericarditis. No pericardial fluid was present. When we separated the pericardium, we found a cyst on the anterolateral surface of the heart, over the left anterior descending coronary artery (LAD) (Fig. 1A). To avoid damage to the heart, particularly the LAD, we decided to arrest the heart in order to remove the cyst. Cardiopulmonary bypass was instituted and the aorta was cross-clamped. Heart arrest and myocardial preservation were maintained with use of alternating retrograde–antegrade blood cardioplegia. Although the cyst was adherent to the epicardium, we were able to excise it intact without damaging the LAD. Aortic and mitral valve replacement using bileaflet prosthetic valves was performed, preserving the posterior leaflet of the mitral valve. On gross examination, the cyst measured 5 × 4 × 2.5 cm, was semitransparent, unilocular, and bosselated (this last due to multiple constricting fibrous bands) (Fig. 1B). Most of the wall was thin, except for the part that was in contact with the epicardium, which was thicker, possibly due to adhesions. Microscopically, the cystic wall was fibrotic and lined by a single layer of cells of a mesothelial type (Fig. 2). Immunohistochemical stains showed these cells to be positive for pancytokeratin and calretinin, which supported their mesothelial origin. A diagnosis of benign mesothelial cyst was made. The postoperative period was uneventful. The patient's condition improved after the operation, and she was discharged on the 7th postoperative day without complications. The patient was asymptomatic upon follow-up 6 months after surgery.

Fig. 1 A) Intraoperative view of the pericardial cyst over the left anterior descending coronary artery. Note also that the cyst originates from epicardium. B) Gross appearance of the cyst demonstrates fibrous bands.

Fig. 2 Microscopic view of the cyst (H&E orig. ×200).

Comment

Pericardial cysts are uncommon benign lesions that have a worldwide incidence of 1 per 100,000.⁸ They are usually located at the cardiophrenic angles, more often on the right side. In 8% to 11% of patients, the cysts are located elsewhere: in the posterior mediastinum, the right or left hilar region, the right paratracheal area, or in the vicinity of the aortic arch.^3,9 Cysts originating from the epicardium are extremely rare, with only 4 cases reported until now.^4–7 Pericardial cysts are generally detected on routine radiologic studies or incidentally in the operating room. These cysts are often asymptomatic, unless they reach a large size and cause compression-related symptoms. There are no findings on physical examination that suggest the presence of a pericardial cyst. The cysts are commonly unilocular, but they may appear to be multilocular due to constrictive fibrous bands. They are either congenital or acquired. A previous episode of pericarditis due to rheumatic fever might have been the cause of the cyst detected in our patient. We believe that “benign mesothelial cyst” is a more appropriate term to describe these cysts, because “pericardial cyst” denotes only location and may incorrectly encompass such entities as cystic lymphangioma.

Long-term follow-up studies have shown that most patients remain without symptoms. Surgical excision becomes mandatory when the cyst is symptomatic, infected, or possibly malignant; grows progressively or achieves giant dimensions;¹⁰ compresses important structures; or is atypical in location or other characteristics.

Although the pericardium was adherent to the heart in our patient, the cyst originated from the epicardium and not from the parietal pericardium (Fig. 1). Cardiopulmonary bypass may be required when cysts compress surrounding structures or erode the ventricular wall.^7,10 In our patient, excision was complicated because the cyst was located over the LAD. Furthermore, adhesions over the epicardium made it difficult for us to see the LAD. To avoid injury to the LAD, we decided to operate with the patient under cardiopulmonary bypass.